How to unmount external / internal devices in Linux :-
Unmounting is done with the umount command. No, I didn't make a typo: the command really is umount, not unmount.
When unmounting, you'll need to tell umount what mounted device to unmount, either by telling what's the device or the mount point. For example, if /dev/fd0 is mounted to /mnt/floppy, you'll unmount it with
$ umount /mnt/floppy
$ umount /dev/fd0
It's not wise to remove the floppy from the floppy drive without unmounting it first! In the worst case the data you were writing to the floppy wasn't written into it yet. With CD-ROMs you can't do this: the tray won't even open if you haven't unmounted the CD first.